1. Field of the Invention
This invention covers the field of medicine, in particular, biochemistry and biomaterials extraction technology and is also used for manufacturing of biomaterials applied as a plastic material by the operative restoration of bone defects by destruction of bone tissue, cystectomy, oncotomy and also as a carrier of active substances and drugs, in plastic surgery by restoration of organ's or tissue's volume.
2. Description of the Related Art
A bone is a living tissue, in which a continuous reorganization process including a simultaneous destruction and restoration of the bone material. Old tissue is remodulated during a normal process and also by implantation of a foreign material, new tissue is formed in place of this. Equilibrium is permanently maintained between the quantity of a reformed bone and a newly developed bone. This process will go easier if the implanted material is close to a habitual bone in its structure.
That is why at present it is preferred to prepare the substitute material from tissues of a natural bone, which must be of animal origin by reasons of ethics and practice.
It is well-known that a partial demineralization promotes implantation of a bone graft. Hereupon various additional steps are taken, which are intended either for full deproteinization of the bone or for influencing the nature of proteins remaining bound in the bone base or for increase of this share of proteins.
As regards to methods used heretofore, in particular, the U.S. Pat. No. 4,394,370 can be given as an example, where it is proposed to form a spongy mass by the melting of a mixture consisting of a powder of the demineralized bone of human origin and a diluted collagenic powder with the help of glutaraldehydic binding providing a cross-link.
The U.S. Pat. No. 4,743,259 combines demineralization by hydrochloric acid with enrichment by proteins carried out on the first part of the demineralized bone with the help of proteins extracted from the second part with use of guanidine.
Furthermore, it is proposed in patent application FR No. 2582517 to process bone ends taken from animals, namely, from livestock by means of a partial demineralization and tanning with use of glutaraldehyde. Bone fragments to be implanted by a surgeon are cut out with necessary shaping from cattle's bones after a preliminary pretreatment including delipidization or defatting operation with the use of an organic solvent such as ethanol, demineralization with the use of calcium extraction means such as hydrochloric acid and an operation providing for tanning with glutaraldehyde and also various washing operations.
It is obvious from the description of the prior art patents given above that the mentioned tanning process favors the features of a treated bone, as it facilitates the cross-linkage of macromolecular chains. However, it has been recently detected that the treatment of glutaraldehydes does not result in a significant reduction of immunogenic features and, moreover, the engraftment of the implanted bone occurs in a desirable degree, as opposed to the theory suggested earlier. Furthermore, such chemical compounds like glutaraldehyde have a disadvantage in that they are biologically toxic.
A method for obtaining a material for osteoplasty from the bone tissue of natural origin including the subsequent removal of lipids from the natural bone tissue with use of an organic solution, selective extraction with the subsequent washing and lyophilization of the end product is known, characterized by the selective extraction carried out with the use of a urea solution for denaturation and removal of antigenic proteins with the maintaining of a non-denaturated collagen of type I in a natural form located in the initial mineral bone structure and the obtained structure is directed to washing and lyophilization (RU No. 2104703, A61K35/32, publ. Feb. 20, 1998).
Therefore, the removal of lipids is carried out with use of the organic solution containing 10 volumetric parts of chloroform/methanol or ethanol/dichloromethane mixture per 1 part of bone in proportion 2:3-1:3 accordingly. The demineralization of the bone tissue is carried out with the solution of the hydrochloric acid with molarity of 0.1-1.0 M after removal of lipids. The extraction with an ionic solvent is carried out before the selective extraction, in particular, with use of sodium chloride.
The selective extraction is conducted with a 2 to 10 M urea solution, preferably with a 5 to 8 M solution or aqueous urea solution containing 0.1-0.5 vol. of mercaptoethanol. The washing is carried out with use of distilled water at 30-60° C., preferably at 45-55° C. Alternatively, the selective extraction is carried out first with use of the urea solution in concentration from 2 to 10 M, preferably within the limits of 5 to 8 M, then, after washing, with use of the aqueous urea solution containing mercaptoethanol in quantity of 0.1 to 0.5 vol. in the solution.
The material for osteoplasty obtained by such a way represents a compound, in which the bone structure of natural origin containing 20-40% (namely 25-35%) of a non-denaturated collagen of type I is maintained. According to analysis results of dry material, this material contains less than 15% lipids, 25-45% proteins, 10-30% calcium, 5-20% phosphorus and has a water content below 10% and a Ca/P ratio in preference from 1 to 2.2.
The material can have a shape of parallelepipedic blocks, truncated pyramids, plates, discs or powder amalgamated with a binder which can preferably be of biological origin such as fibrin or synthetic origin such as, for example, synthetic biodegradable polymer.
This invention is chosen as a prototype both for the method and material, as it is the closest to the proposed invention as regards to its engineering solution.
The disadvantage of the mentioned method is the fact that such treatment, although it maintains a bone collagen of type 1 in the natural form, does not provide full removal of antigens such as non-collagenic proteins, lipids, lipoproteins and other substances reducing the biocompatibility of the obtained material from this tissue.